1. Field of the Invention
The present invention is broadly concerned with an in vivo method of reducing reperfusion injury in a mammal resulting from temporary occlusion of a blood vessel and subsequent reperfusion thereof; the method comprises administration of certain proline and arginine-rich peptides to the mammal's bloodstream which lessen the potentially damaging effect of reperfusion. More particularly, the invention pertains to such a method wherein, in preferred forms, peptides having up to about 50 amino acid residues therein and one or more amino acid sequences --PXXP-- where P is proline and X is any amino acid are administered to the bloodstream of a mammal so as to effectively contact the blood vessels and inhibit indices of reperfusion injury, i.e., production of reactive oxygen species, neutrophil adherence to endothelium and extravasation of neutrophils as a result of reperfusion.
2. Description of the Prior Art
In the course of some surgical procedures such as coronary bypass and organ transplantation surgery, blood vessels are intentionally occluded to allow the surgeon free access to the surgical site, whereupon the occlusion is removed and reperfusion of blood occurs. In addition, some patients with coronary or peripheral vascular disease are exposed to regular ischemia-reperfusion cycles (angina pectoris or intermittent claudication) that terminates spontaneously or in response to administered drugs. In this connection, it has been found that reperfusion is the cause of tissue damage, i.e., ischemic tissue prior to reperfusion is essentially undamaged, but will often experience massive, irreversible degradation such as cell death and tissue necrosis upon reperfusion. It is believed that the readmission of blood and oxygen during reperfusion promotes the release of oxygen-derived free radicals, and that this mechanism is a prime cause of tissue damage. Ischemia also disrupts the handling of oxygen by the mitochondrial electron transport systems and enzymes such as xanthine oxidase. Upon reperfusion, there is a rapid increase in free radical activity, probably amplified by transition metal ions released by ischemic cells. Subsequent damage to the sarcoplasmic reticulum and other membranes impairs handling of calcium and other ions, a hallmark of reperfusion injury. It has also been observed that reperfusion injury may occur over a period of several days (up to 5 days) time after reperfusion is begun, with the most extensive tissue damage occurring within the first 1-2 days. After blood flow has continued for 5 days, the reperfusion event is generally deemed concluded, and subsequent blood flow does not cause additional tissue damage.
Thus, reperfusion of tissues following ischemia leads to an array of biochemical events which can culminate in oxidative damage to cell structures. It is believed that reactive oxygen species such as superoxide ion are central to these events. It is also known that a major source of reactive oxygen intermediates are neutrophils.
PCT Publication WO 96/09322 entitled Synducin Mediated Modulation of Tissue Repair describes the use of PR-39 and related peptides for inducing the expression of proteoglycans, called syndecans, in mesenchymal cells. The reference suggests that the peptides can be administered after tissue death due to starvation in order to promote neovascularization. Accordingly, this reference postulates that damaged tissues can be partially restored via neovascularization long after ischemic damage and tissue death occurs. However, there is no suggestion of prevention or amelioration of reperfusion injury by any means; moreover, the reference does not teach administration of peptides into the bloodstream.
There is accordingly a need in the art for an in vivo method of reducing the extent of reperfusion injury which would othervise result from reperfusion of a temporarily occluded mammalian blood vessel.